G protein-coupled receptors (GPCRs) including those for catecholamines and angiotensin II regulate vascular reactivity, including vasoconstriction and vasodilation, as well as vascular smooth muscle (VSM) cell mitogenesis and migration. Vascular reactivity may be perturbed in hypertension, whereas altered VSM mitogenesis and migration characterize pathological intimal hyperplasia following surgical bypass or restenosis after arterial angioplasty. Following GPCR activation, GPCRs are phosphorylated by one of seven GPCR kinases (GRKs) and then one of two isoforms of b-arrestin is recruited to the receptor. b-arrestin binding sterically interdicts further signaling to G proteins, leading to receptor desensitization and attenuation of signaling. b-arrestins also play positive roles in signaling, serving as adapters and scaffolds to organize GPCR- mediated activation of MAP kinase cascades, such as the extracellular signal regulated kinases (ERK 1/2). These MAP kinases regulate mitogenesis and migration of VSM cells and other cell types. Our group has developed mice in which the GRKs and b-arrestins have been individually knocked out. We will utilize these animals, and VSM cells from them, to test the central hypothesis that regulation of GPCR signaling by b-arrestins and GRKs is critical for normal vascular homeostasis. Our specific aims are 1) To elucidate the vascular phenotype of b-arrestin and GRK knockout mice by analyzing conscious and anesthetized blood pressure responses and vascular reactivity using isolated aortic rings; 2) To elucidate the roles of b-arrestins and GRKs in signaling via endogenous GPCRs in isolated arterial and venous VSM cells from wild type and knockout mice by determining both A) the specificity of b-arrestins and GRKs in desensitizing second messenger signaling via endogenous GPCRs and B) the roles of b-arrestins and GRKs in GPCR stimulated ERK activation, proliferation, and migration of VSM cells; and 3) To determine if the loss of specific b-arrestins or GRKs alters in vivo proliferative intimal hyperplasia following mouse vein-graft surgery or arterial injury. These experiments have the potential to lead to the development of new strategies for limiting vein graft failure and restenosis.